EXISTS 在SQL語(yǔ)句中怎么用？

EXISTS
指定一個(gè)子查詢，檢測(cè)行的存在。
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SELECT DISTINCT name
FROM student
WHERE EXISTS
(SELECT *
FROM register
WHERE id = student.id);

(note that if some rows in student register.id =student.id, all those rows in student are selected out.)